1. Field of the Invention
This invention is related to a pane, in particular a laminated pane, for automobiles, for example, equipped with electrical conductors serving as an antenna inside the pane.
2. Description of the Related Art
It is known, notably from Patent Application EP-0 325 510, to embed metal wires in the intermediate film of plastic material in a laminated pane. These metal wires can serve as a radio antenna for frequencies which in general do not exceed 3 GHz. For the reception or transmission of signals having a higher frequency, and notably of ultra high frequency signals, these antenna made from metal wires are no longer effective. For these frequencies, it is known to use metal surfaces termed microstrips or "pellets". On the other hand, this microstrip is not always sufficient and should advantageously be associated with an earth (ground) plane which is a conducting film of larger area. These two films are then separated from each other by a dielectric.
To improve reception, it is also possible to associate several microstrips connected in accordance with the techniques known to the person skilled in the art.
At present this type of frequency and, more especially, the 5795-5815 MHz, 63-64 GHz and 74-77 GHz bands, are used notably for vehicle-route communications, in particular for recognition of the vehicles and authentication of payment when the vehicles pass a remote toll charging station. These devices in development consist of disposing a casing behind the windscreen, this casing containing the antenna and being connected to a device enabling information to be received and instructions to be transmitted, notably payment instructions. It comprises, for example, a signal processing unit such as a keyboard associated with a screen. This latter device may be integrated into the vehicle dashboard, while in contrast the casing containing the antenna remains visible because it must be held at an orientation, defined by the transmitter, which enables the signal to be received while passing in front of this transmitter.
Another disadvantage associated with this device may be bad reception of the signal, or indeed impossibility of reception in the case where the windscreen possesses a film based upon a metallic oxide such as a reflective film. The signal is then in effect at least partly attenuated.